1. Field of the Invention
This invention relates to a method and apparatus for accessing data in a lattice array storage device. It is particularly, but not exclusively, adapted to be used in connection with such an array wherein data storage is implemented by magnetic bubble domains. The proper classification for the subject matter of this invention is believed to be Class 340, Subclass 174TF.
2. Description of the Prior Art
A recent development in the relatively new field of technology wherein magnetic bubble domains are used for the storage and manipulation of data has been the orderly arrangement of such bubble domains in a confined lattice array. Such an array may be generally likened to a crystaline lattice structure, and is characterized by the bubble domains being so closely packed that the interactions between them, i.e., the forces of repulsion since they all have the same magnetic orientation, cause their orderly arrangement in a hexagonal configuration wherein each bubble domain has six nearest neighbors. The outline or boundary of the array has the shape of a 60.degree. rhombus. The bubble domains may be coded in a number of ways to represent information or data bits, and they may be manipulated in various ways to implement data processing functions. A system using a lattice storage device of this type is disclosed in co-pending application Ser. No. 395,336 filed Sept. 7, 1973, now abandoned in favor of continuation application Ser. No. 632,604 filed Nov. 14, 1975. It was also described in a series of technical papers presented at the 20th annual conference on magnetism and Magnetic Materials which was held in San Francisco, Calif., Dec. 3-6, 1974.
One of the problems associated with lattice arrays is the accessing of the data stored therein, and its extraction for reading and processing purposes. The magnitude of the problem may be readily appreciated when it is considered that the diameter of an individual bubble domain may be less than 1 micron, the data word desired may lie in the central area of the array, and if it is somehow simply lifted out or removed in situ the surrounding bubble domains will close in to fill the void and thus destroy the storage order of the array.
The accessing technique employed in the above mentioned application involves the translation of the desired data column across the array until it reaches the reading position at the output side of the array. The earlier columns that precede it are read out and reinserted at the input side. This amounts to "revolving" the entire storage file, and can be very time consuming unless the desired column handly happens to be proximate the output side of the array.
Another accessing technique employed for lattice arrays is disclosed in co-pending application Ser. No. 429,601 filed Jan. 2, 1974. In this application a plurality of columnar aligned read-write stations are spaced along opposite edges of the lattice array, and buffer regions are provided adjacent to the other set of opposing edges. To access a desired column it need only be translated to the nearest read-write location, where it is then serially pumped out of the array in a direction transverse to the translation direction. Array disturbances caused by the limited translational movements are absorbed in the buffer regions. The column of bubbles which has been read out may be reinserted into its original position in the array through the accessed write station, to thus restore the storage order of the array. While this technique reduces the access time it does so at the expense of increased hardware requirements, since clearly the greater the number of read-write stations the lower the average access time and the worst case access time.